The major objective of the Diabetes Prevention Trial Type I (DPT-1) is to determine whether early intervention by antigen based therapies in non- diabetic relatives of persons with IDDM can delay their development of IDDM as a clinical disease. To determine whether early intervention with parenteral insulin therapy consisting of periodic courses of intravenous insulin with accompanying chronic daily subcutaneous injections of long lasting (Ultralente) recombinant human insulin, will delay or prevent the development of clinical IDDM in "high risk" (i.e. 350% risk over 5 years) non-diabetic relatives of patients with IDDM. This intervention in the experimental group will be compared with a standard group who will have close observation and early initiation of treatment at first evidence of clinical IDDM. To determine whether intervention with repeated oral administrations of potential autoantigens (e.g. human insulin crystals), given extremely early in the "intermediate risk" (i.e. 15-50% risk over 5 years) non- diabetic relatives of patients with IDDM. This intervention will be compared with placebo given in a double-masked fashion.